Derivative Instruments (Credit Derivatives Sold) (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Credit Default Swap [Member]
Derivative [Line Items]
Weighted average remaining expected maturity	1 year 1 month 6 days	1 year 7 months 6 days
Insured Swaps [Member]
Derivative [Line Items]
Weighted average remaining expected maturity	16 years 10 months 24 days	16 years 8 months 12 days
Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	$ 11,889	$ 13,525
Total fair value of credit derivatives	(147)	(246)
Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	8,016	9,481
Total fair value of credit derivatives	(144)	(244)
Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	3,873	4,044
Total fair value of credit derivatives	(3)	(2)
Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount	0	0
Total fair value of credit derivatives	0	0
Credit Rating Aaa [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	5,823	6,914
Total fair value of credit derivatives	(2)	(2)
Credit Rating Aaa [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	5,823	6,914
Credit Rating Aaa [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	0	0
Credit Rating Aaa [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount	0	0
Credit Rating Aa [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	113	363
Total fair value of credit derivatives	0	0
Credit Rating Aa [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	0	246
Credit Rating Aa [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	113	117
Credit Rating Aa [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount	0	0
Credit Rating A [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	3,745	3,903
Total fair value of credit derivatives	(3)	(2)
Credit Rating A [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	968	968
Credit Rating A [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	2,777	2,935
Credit Rating A [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount	0	0
Credit Rating Bbb [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	1,114	1,163
Total fair value of credit derivatives	(2)	(2)
Credit Rating Bbb [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	152	193
Credit Rating Bbb [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	962	970
Credit Rating Bbb [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount	0	0
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member]
Derivative [Line Items]
Derivative notional amount	1,094	1,182
Total fair value of credit derivatives	(140)	(240)
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Derivative notional amount	1,073	1,160
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Insured Swaps [Member]
Derivative [Line Items]
Derivative notional amount	21	22
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative notional amount	$ 0	$ 0